Re: [PATCH 3/3] nfs: Store and use inode in nfs_open_context

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On Fri, Mar 4, 2016 at 5:17 AM, Miklos Szeredi <miklos@xxxxxxxxxx> wrote:
> On Thu, Mar 03, 2016 at 09:16:33AM +0100, Miklos Szeredi wrote:
>> My plan was to introduce a file_dentry() helper that MUST be used by
>> filesystems to get the dentry from the file and that makes sure it's
>> the right one (check against file_inode()).   If not, then we could
>> call into overlayfs to return the right one, similar to
>> ->d_select_inode(), except we want to have a dentry and we want to
>> have *a particular dentry* matching file_inode() (the file could have
>> been copied up in the mean time).
>
> Something like the following (untested, against overlayfs-next.git)
>
> Thanks,
> Miklos
>
> ---
>  fs/nfs/dir.c           |    6 +++---
>  fs/nfs/inode.c         |    2 +-
>  fs/nfs/nfs4file.c      |    4 ++--
>  fs/open.c              |   11 +++++++++++
>  fs/overlayfs/super.c   |   16 ++++++++++++++++
>  include/linux/dcache.h |    1 +
>  include/linux/fs.h     |    2 ++
>  7 files changed, 36 insertions(+), 6 deletions(-)
>
> --- a/fs/nfs/dir.c
> +++ b/fs/nfs/dir.c
> @@ -377,7 +377,7 @@ int nfs_readdir_xdr_filler(struct page *
>   again:
>         timestamp = jiffies;
>         gencount = nfs_inc_attr_generation_counter();
> -       error = NFS_PROTO(inode)->readdir(file->f_path.dentry, cred, entry->cookie, pages,
> +       error = NFS_PROTO(inode)->readdir(file_dentry(file), cred, entry->cookie, pages,
>                                           NFS_SERVER(inode)->dtsize, desc->plus);
>         if (error < 0) {
>                 /* We requested READDIRPLUS, but the server doesn't grok it */
> @@ -560,7 +560,7 @@ int nfs_readdir_page_filler(nfs_readdir_
>                 count++;
>
>                 if (desc->plus != 0)
> -                       nfs_prime_dcache(desc->file->f_path.dentry, entry);
> +                       nfs_prime_dcache(file_dentry(desc->file), entry);
>
>                 status = nfs_readdir_add_to_array(entry, page);
>                 if (status != 0)
> @@ -864,7 +864,7 @@ static bool nfs_dir_mapping_need_revalid
>   */
>  static int nfs_readdir(struct file *file, struct dir_context *ctx)
>  {
> -       struct dentry   *dentry = file->f_path.dentry;
> +       struct dentry   *dentry = file_dentry(file);
>         struct inode    *inode = d_inode(dentry);
>         nfs_readdir_descriptor_t my_desc,
>                         *desc = &my_desc;
> --- a/fs/nfs/inode.c
> +++ b/fs/nfs/inode.c
> @@ -940,7 +940,7 @@ int nfs_open(struct inode *inode, struct
>  {
>         struct nfs_open_context *ctx;
>
> -       ctx = alloc_nfs_open_context(filp->f_path.dentry, filp->f_mode);
> +       ctx = alloc_nfs_open_context(file_dentry(filp), filp->f_mode);
>         if (IS_ERR(ctx))
>                 return PTR_ERR(ctx);
>         nfs_file_set_open_context(filp, ctx);
> --- a/fs/nfs/nfs4file.c
> +++ b/fs/nfs/nfs4file.c
> @@ -26,7 +26,7 @@ static int
>  nfs4_file_open(struct inode *inode, struct file *filp)
>  {
>         struct nfs_open_context *ctx;
> -       struct dentry *dentry = filp->f_path.dentry;
> +       struct dentry *dentry = file_dentry(filp);
>         struct dentry *parent = NULL;
>         struct inode *dir;
>         unsigned openflags = filp->f_flags;
> @@ -57,7 +57,7 @@ nfs4_file_open(struct inode *inode, stru
>         parent = dget_parent(dentry);
>         dir = d_inode(parent);
>
> -       ctx = alloc_nfs_open_context(filp->f_path.dentry, filp->f_mode);
> +       ctx = alloc_nfs_open_context(file_dentry(filp), filp->f_mode);
>         err = PTR_ERR(ctx);
>         if (IS_ERR(ctx))
>                 goto out;
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1234,6 +1234,8 @@ static inline struct inode *file_inode(c
>         return f->f_inode;
>  }
>
> +extern struct dentry *file_dentry(const struct file *file);
> +
>  static inline int locks_lock_file_wait(struct file *filp, struct file_lock *fl)
>  {
>         return locks_lock_inode_wait(file_inode(filp), fl);
> --- a/fs/open.c
> +++ b/fs/open.c
> @@ -831,6 +831,17 @@ char *file_path(struct file *filp, char
>  }
>  EXPORT_SYMBOL(file_path);
>
> +struct dentry *file_dentry(const struct file *file)
> +{
> +       struct dentry *dentry = file->f_path.dentry;
> +
> +       if (d_inode(dentry) == file_inode(file))
> +               return dentry;
> +       else
> +               return dentry->d_op->d_select_dentry(dentry, file_inode(file));
> +}
> +EXPORT_SYMBOL(file_dentry);
> +
>  /**
>   * vfs_open - open the file at the given path
>   * @path: path to open
> --- a/fs/overlayfs/super.c
> +++ b/fs/overlayfs/super.c
> @@ -336,14 +336,30 @@ static int ovl_dentry_weak_revalidate(st
>         return ret;
>  }
>
> +static struct dentry *ovl_d_select_dentry(struct dentry *dentry,
> +                                        struct inode *inode)
> +{
> +       struct ovl_entry *oe = dentry->d_fsdata;
> +       struct dentry *realentry = ovl_upperdentry_dereference(oe);
> +
> +       if (realentry && inode == d_inode(realentry))
> +               return realentry;
> +       realentry = __ovl_dentry_lower(oe);
> +       if (realentry && inode == d_inode(realentry))
> +               return realentry;
> +       BUG();
> +}
> +
>  static const struct dentry_operations ovl_dentry_operations = {
>         .d_release = ovl_dentry_release,
>         .d_select_inode = ovl_d_select_inode,
> +       .d_select_dentry = ovl_d_select_dentry,
>  };
>
>  static const struct dentry_operations ovl_reval_dentry_operations = {
>         .d_release = ovl_dentry_release,
>         .d_select_inode = ovl_d_select_inode,
> +       .d_select_dentry = ovl_d_select_dentry,
>         .d_revalidate = ovl_dentry_revalidate,
>         .d_weak_revalidate = ovl_dentry_weak_revalidate,
>  };
> --- a/include/linux/dcache.h
> +++ b/include/linux/dcache.h
> @@ -161,6 +161,7 @@ struct dentry_operations {
>         struct vfsmount *(*d_automount)(struct path *);
>         int (*d_manage)(struct dentry *, bool);
>         struct inode *(*d_select_inode)(struct dentry *, unsigned);
> +       struct dentry *(*d_select_dentry)(struct dentry *, struct inode *);
>  } ____cacheline_aligned;
>
>  /*

Thanks Miklos! That looks reasonable, assuming it tests out correctly.

Cheers
  Trond
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